1. Field of the Invention
The present invention relates to a multiple-panel liquid crystal display (LCD) device and an image display system using the same. In particular, the present invention relates to a direct-view type LCD device including a multiple LCD panels by which a higher contrast ratio can be obtained. In addition, the present invention relates to an electronic apparatus, an image signal transmitter, an image data switching apparatus, an image data diagnosis apparatus, and a building, in which such a LCD device is used.
2. Description of the Related Art
LCD devices have the advantage of realizing a higher definition with a lower power dissipation and are used for a wide range of applications from a small-screen cellular phone to a large-screen television monitor. However, there is a defect in the LCD device that the contrast ratio of the LCD panel alone in a dark environment is lower than that of a CRT, that (3000:1) of a plasma display panel, which are also used as a television monitor similarly to the LCD panel, and that of a field-emission display panel called FED/SED, and is at most on the order of 1000:1. Therefore, there is pointed out the problem of insufficient feeling of live performance during representing image sources such as a motion picture having a higher power of expression especially in the dark environment.
In order to solve the above problem, there has been developed a technology for controlling the light intensity of the backlight according to the image to be displayed, thereby improving the contrast ratio on the display screen, with the contrast ratio of the LCD panel itself being left intact. In a conventional backlight unit having a surface-emission light source, however, a cold-cathode tube having a narrow dynamic range is used as the light source. Thus, improvement of the contrast ratio by controlling the light intensity of the backlight according to the image to be displayed is limited to around 2000 to 3000:1.
It is to be noted that the cold-cathode tube of the backlight unit has a shape of rod. Thus, if there are a high luminance area and a low luminance area concurrently represented on the same screen of the LCD device, the luminance of the backlight cannot be regulated area by area, resulting in a poor improvement of the contrast ratio obtained by the luminance control of the backlight. Therefore, if the image represented on the screen has a higher luminance area and yet is desired to emphasize the reproducibility in the lower luminance area, the effective contrast ratio is lowered due to the presence of the higher luminance area.
In order to solve the above problems, the contrast ratio of the LCD panel should be drastically improved. However, as described before, the contrast ratio of the LCD panel alone is at most about 1000:1. Techniques for manufacturing LCD devices capable of remarkably improving the contrast ratio thereof without improving the contrast ratio of the LCD panel itself are described, for example, in Patent Publications JP-1989-10223A and JUM-1984-189625A.
FIG. 11 shows the configuration of a LCD device having a structure of multiple-panel LCD device wherein two LCD panels are stacked one on another. The LCD device 900 includes a polarizing film 901, a LCD panel 941, a polarizing film 902, a LCD panel 942, and a polarizing film 903, which are arranged in this order from the light incidence side toward the light emitting side of the LCD device 900, i.e., the rear side toward the font side of the LCD device 900. The LCD panel 941 includes a liquid crystal (LC) layer 931 operating in a twisted-nematic (TN) mode, and a pair of transparent substrates 911 and 912 having transparent electrodes 921 and 922 on the surface thereof near the LC layer 931. The LCD panel 942 includes a LC layer 932 operating in a TN mode, and a pair of transparent substrates 913 and 914 having transparent electrodes 923 and 924 on the surface thereof near the LC layer 932. The transparent electrodes 921 and 923 of the LCD panels 941 and 942 are a pixel electrode to which a driving signal is supplied from a driving circuit 951. The transparent electrodes 922 and 924 are a common electrode. By adopting the above structure including two stacked LCD panels, when the contrast ratio is measured by using laser light, the contrast ratio, which is around 10 to 15 in the structure using a single LCD panel, can be improved up to around 100:1. Further, the contrast ratio can be improved to around 1000:1 by stacking three LCD panels. In this manner, a contrast ratio exceeding the limit of the contrast of the LCD panel alone can be realized.
Patent Publication JP-1989-10223A describes a driving scheme wherein two of the stacked LCD panels 941 and 942 are driven by the same signal supplied from a single signal source to obtain a higher contrast ratio. However, in the structure of LCD device 900, the LC layers 931 and 932 are stacked apart from each other with a distance or gap d1 in the thickness direction. Therefore, when the display screen is observed in a slanted viewing direction, a misalignment occurs in the pixel between the LCD panel 941 and the LCD panel 942. Due to this misalignment, if the observer observes the screen in a slanted viewing direction, the image will be observed as double lines, which cause the observer to feel a sense of discomfort. In addition, when two LCD panels performing color display are stacked one on another and observed in a slanted viewing direction, the light may pass through different color filters between the rear-side LCD panel and the front-side LCD panel. For this reason, there occurs a problem in that the luminance and visibility of the stacked-panel LCD device is lowered.